A printed circuit board (PCB) is formed by printing a circuit line pattern at an electrical insulating substrate with a conductive material such as copper, and thus the PCB refers to a board just before electronic components are mounted thereon. That is, in order to densely mount various types of electronic components on a planar surface, the PCB refers to a circuit board having a planar surface on which a mounting position of each component is fixed and a circuit pattern connecting the components is fixedly printed.
In general, a surface processing method for a circuit pattern included in the above-described PCB uses an organic solderability preservative (OSP) method, an electrolytic nickel/gold method, an electrolytic nickel/gold-cobalt alloy method, an electroless nickel/palladium/gold method, etc.
Here, the above-described surface processing methods vary depending on a use thereof, and the use includes, for example, soldering, wire bonding, and a connector.
FIG. 1 is a view illustrating a printed circuit board according to the related art.
Referring to FIG. 1, a printed circuit board 10 includes a plurality of insulating layers 11, a circuit pattern 12 disposed at a surface of the plurality of insulating layers 11, and a via 13 configured to pass through at least one among the plurality of insulating layers 11 and electrically connect circuit patterns disposed at different layers.
In addition, a first pad 14 is disposed on an insulating layer disposed at an uppermost layer among the plurality of insulating layers 11, and an upper conductive layer 15 is disposed on the first pad 14.
Further, a second pad 16 is disposed under an insulating layer disposed at a lowermost layer among the plurality of insulating layers 11, and a lower conductive layer 17 is disposed under the second pad 16.
Furthermore, a protective layer 18 having an opening, through which at least a part of a surface of the lower conductive layer 17 is exposed, is disposed under the insulating layer disposed at the lowermost layer.
In the above-described printed circuit board 10, pads having different functions are disposed at the uppermost and lowermost portions of the plurality of insulating layers 11, respectively. That is, the first pad 14 may be a pad for wire bonding, which is electrically connected to an electronic component (not shown) via a wire. In addition, the second pad 16 may be a pad for soldering, which is electrically connected to an external substrate via an adhesive member (not shown).
The upper conductive layer 15 and the lower conductive layer 17 are disposed at surfaces of the first pad 14 and the second pad 16, respectively. The upper conductive layer 15 and the lower conductive layer 17 are disposed to perform wire bonding or soldering together with a purpose of inhibiting oxidation of the pad.
However, although thicknesses of the upper conductive layer and the lower conductive layer are different depending on the use of the pad, the upper conductive layer 15 and the lower conductive layer 17 are formed to have the same thickness in the related art. At this point, the upper conductive layer 15 and the lower conductive layer 17 generally include gold (Au). Therefore, in the related art, the thickness of the lower conductive layer 17 is formed based on the thickness required for the upper conductive layer 15, so that there is a problem that a manufacturing cost due to unnecessary consumption of gold is increased. Further, in the related art, in order to reduce a plating thickness of the upper conductive layer or the lower conductive layer including gold, copper/nickel is mainly formed as an underlying layer, so that there is a problem that a product thickness increases due to an increase in the layer.